I don't do a lot of gluten-free baking, but have done a little. A friend who had her own cake shop said she just subs the flours in her usual recipes. Now, while I have had some success with that, it doesn't always work.

There is a new product available at Williams-Sonoma called Cup4Cup that is a flour substitute that supposed to be very good. I haven't tried it myself yet, but did speak to the people at the Fancy Food Show this year, and they said it works great. It was developed and used by The French Laundry, so it might be a good place to start experimenting on a cake.